/Engine/Source/Runtime/Core/Public/ProfilingDebugging/ResourceSize.h
Add anotherFResourceSizeExto this one.
[FResourceSizeEx](API\Runtime\Core\ProfilingDebugging\FResourceSizeEx) & operator+= ( const [FResourceSizeEx](API\Runtime\Core\ProfilingDebugging\FResourceSizeEx) & InRHS )